Roof construction presents many problems. The roof must be waterproof so that rainwater and melting snow and ice cannot enter the building. In most geographic areas insulation of the roof presents further problems. The roof must be insulated to prevent loss of heat in cold weather when the building is heated, and to prevent entrance of heat in hot weather when the building is air conditioned. Waterproofing and insulation of roofs introduce another problem in that moisture from within the building must no be allowed to condense on the undersurface of a roof, or within the insulation. In addition, the roof surface must be capable of bearing a certain amount of traffic. This may be a very light amount when traffic is necessary only for repairs, or it may be rather heavy traffic in areas where the roof serves as a passageway for access to facilities that must be serviced frequently. In many areas the roof must also be proof against penetration by icicles that may drop from a very substantial height, such as from taller nearby buildings, or from towers above the roof.
Various efforts have been made to solve the above and other problems in roof construction. It is common practice to provide a waterproof membrane on top of a roof deck, which membrane may be a single layer of plastic resin or elastomeric material. or which may be built-up of a plurality of layers of suitable fabric or paper combined with asphalt or bitumen. Suitable insulating material is then placed below the roofing deck and a waterproof membrane or the like is placed beneath the insulation to prevent water vapor in the building from penetrating the insulation.
Alternatively, there is a known built-up roof construction in which a waterproof membrane is placed directly on or above the roof deck to prevent moisture from passing in either direction. Panels of rigid foam insulation then are applied above the membrane. Protection may be provided for the plastic material such as by separate concrete slabs or panels, by roofing gravel, or by a continuous layer of concrete poured on the site.